1. Field of the Invention
The present invention relates to a fluid mixer for supplying a fixed amount of fluid flowing through at least two supply lines to a mixing line in a fluid transportation in various industries including chemical plants, semiconductor manufacture, food area, bio-related area, etc., and more particularly, to a fluid mixer which can supply a fixed amount of fluid to the mixing line while maintaining a highly accurate mixing ratio in each of the supply lines even if a pressure on the downstream side of a back pressure valve of the mixing line is fluctuated, and further can change the mixing ratio of the mixing line without pump control of the fluid in the supply lines. The fluid mixer can also change the mixing ratio of the mixing line in the state where the fluid is flowed only by adjusting a flow rate of one of the supply lines.
2. Description of the Related Art
As an example of a conventional fluid mixer is a fluid mixer shown in FIG. 7 (disclosed in Japanese Unexamined Patent Application Publication No. 2000-250634, for example). In this fluid mixer, a pump 102, a constant-pressure control valve 103, an orifice 104, a pressure gauge 105 and a check valve 106 are connected in series to a first supply passage 101 from the upstream side, and to a second supply passage 107, in the same way as the first supply passage 101, a pump 108, a constant-pressure control valve 109, an orifice 110, a pressure gauge 111 and a check valve 112 are connected in series from the upstream side and an in-line type mixer 114 is provided on a mixing passage 113 where the fluids flowing through each of the supply passages are merged.
The action is that the fluid flowing through the first supply passage 101 is fed by pressure by the pump 102 and flows into the constant-pressure control valve 103. The fluid having flowed into the constant-pressure control valve 103 has its pulsation suppressed by the action of the constant-pressure control valve 103 and set to a predetermined pressure and passes through the orifice 104 to flow into the mixing passage 113. At this time, the same action as the fluid in the first supply passage 101 also occurs at the same time in the second passage 107, and the fluid in the second passage 107 flows into the mixing passage 113. The fluids having flowed into the mixing passage 113 and merged are fed to the in-line type mixer 114, where they are stirred and mixed. At this time, the fluid flowing through each of the supply passages 101 and 107 is mixed at a predetermined ratio set in advance at the mixing passage 113 in the state where pulsation is suppressed. Moreover, by the action of the orifices 104 and 110, they are mixed at a predetermined ratio without subjected to pressure fluctuation of the in-line type mixer 114.
However, the above conventional fluid mixer has the following problems:    (1) If a diaphragm part such as nozzle for supply to a use point is provided at the end on the downstream side of the in-line type mixer 114 in the mixing passage 113, adhesion of foreign substances such as air bubbles to the nozzle increases the pressure on the downstream side of the orifices 104 and 110 and causes pressure fluctuation larger than the pressure fluctuation in the in-line type mixer 114. The orifices 104 and 110 can not respond to the pressure fluctuation, and the flow rates are lowered and the accuracy of mixing ratio is deteriorated.    (2) If a valve or the like is provided at the mixing passage 113 for opening/closing, when the pressure of the mixing passage 113 is fluctuated, the flow rates are also lowered as in the above (1) and the accuracy of the mixing ratio is deteriorated.    (3) If the flow rate of the fluid in one of the supply passages is changed so as to change the mixing ratio, the pressure on the downstream side of the orifice 104 or 110 on the other of the supply passage is fluctuated, the same phenomenon as in the above (1) occurs and mixing at a desired mixing ratio can not be realized.